This invention relates generally to hydraulically-actuated systems used with internal combustion engines, and more particularly to an axial piston pump of a high pressure hydraulically-actuated system.
Axial piston pumps are known to be used in hydraulically-actuated fuel injection systems. The efficient operation of such pumps is significant to the overall operation of the engine. Moreover, the ability of such pumps to operate free of maintenance is important to reduce downtime of the system. While efficient operation is an important design criteria, issues such as weight, size, cost, and ease of assembly influence the overall design of such pumps.
U.S. Pat. No. 6,035,828 to Anderson et al. describes a fixed displacement, variable delivery axial piston pump for a hydraulically-actuated fuel injection system. In the system, a high pressure common rail supplies hydraulic working fluid to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The hydraulic fluid received in the common rail is pressurized by the fixed displacement axial piston pump that is driven directly by the engine. The pump includes a plurality of pistons disposed in parallel about a central longitudinal axis of the pump, and reciprocation of the pistons is achieved by the rotation of an angled camming surface or swash plate in continuous contact with the proximal ends of the pistons. The pump housing includes inlet and outlet check valves fluidly coupled to each pump chamber for allowing one way flow of hydraulic fluid into and out of the pump chambers during a pumping stroke of the piston. Displacement of the pump is varied by a control valve that selectively varies the amount of pressurized hydraulic fluid supplied to the pump outlet during the discharge stroke of each piston.
While the Anderson et al. pump performs well in operation, there remains room for improvement. For example, the use of inlet check valves may be too restrictive for effective flow of hydraulic fluid during the entire pump operation. During pump start-up, the inlet check valves may act to impede the flow of the hydraulic fluid because the fluid is colder and thus less viscous. This resistance of the flow of hydraulic fluid into the pump chamber can disrupt the necessary flow of fluid to the high pressure common rail and affect operation of the fuel injectors.
The present invention provides an axial piston pump that avoids some or all of the aforesaid shortcomings in the prior art.
In accordance with one aspect of the invention, a pump includes a stationary pump housing having a housing chamber and a pump shaft extending through a proximal end of the pump housing into the housing chamber and rotatable about a pump shaft longitudinal axis, and a swash plate connected to the pump shaft. The swash plate includes a pump inlet passage having an opening in a surface of the swash plate. A plurality of reciprocating pump pistons are also included with the pump, each pump piston at least partially contained within a respective pump chamber formed in the stationary pump housing and having an axial bore extending therethrough. The axial bore of each pump piston having selective communication with the swash plate surface opening to permit the supply of inlet fluid to the axial bore from the inlet passage. A sealing plate is included with the pump disposed between the swash plate and the plurality of pump pistons and substantially seals the swash plate surface opening from a flow of fluid into the inlet passage from the swash plate surface opening.
According to another aspect of the present invention, a method for reducing the required amount of fluid in a low pressure fluid reservoir located in a housing chamber of a pump includes orienting a pump housing of the pump so that a central longitudinal axis of a shaft of the pump extends substantially in a horizontal plane and providing an inlet passage in a rotating swash plate connected to the pump shaft. The method further includes receiving a low pressure fluid from the low pressure fluid reservoir through the inlet passage from a location elevationally below a first elevational level in the housing chamber and sealing a portion of the inlet passage so that the inlet passage does not receive fluid from above the first elevational level. Fluid is drawn from the low pressure fluid reservoir through the inlet passage and to an axial bore of at least one pump piston during a suction stroke of the at least one pump piston.
According to yet another aspect of the present invention, a hydraulically actuated system includes a pump having a rotating pump shaft having a central longitudinal axis, a rotating swash plate fixed to the pump shaft, and a plurality of non-rotating pump pistons. The pump pistons are at least partially located in pump chambers formed in a housing of the pump. The pump further includes an inlet passage formed in the swash plate having a radially inner opening and a radially outer opening formed in a surface of the swash plate, a sealing plate located between the surface of the swash plate and the plurality of pistons. The sealing plate covers the radially outer opening to block entry of fluid into the inlet passage from the radially outer opening. The pump further includes axial bores in each of the pump pistons for receiving fluid from the inlet passage. The system further includes a high pressure rail connected to the pump, at least one hydraulically actuated fuel injector connected to the high pressure rail, and an electronic control module in communication with and capable of controlling the fluid delivery control assembly.